Coating systems for silicon-containing substrates

Abstract

An article includes a silicon-containing ceramic substrate and a coating system overlying the silicon-containing ceramic substrate. The coating system includes an intermediate coating overlying the silicon-containing ceramic substrate and a barrier coating overlying the intermediate coating. The intermediate coating includes silicon and hafnium disilicide. A coefficient of thermal expansion of the intermediate coat is less than about 7 parts per million (ppm) per degree Kelvin (K).

What is claimed is: 
     
         1 . An article comprising:
 a silicon-containing ceramic substrate; and   a coating system overlying the silicon-containing ceramic substrate, wherein the coating system comprises:
 an intermediate coating overlying the silicon-containing ceramic substrate, wherein the intermediate coating includes silicon (Si) and hafnium disilicide (HfSi 2 ), and wherein a coefficient of thermal expansion (CTE) of the intermediate coating is less than about 7 parts per million (ppm) per degree Kelvin (K); and 
 a barrier coating overlying the intermediate coating. 
   
     
     
         2 . The article of  claim 1 , wherein the intermediate coating further comprises hafnium dioxide (HfO 2 ) and silicon dioxide (SiO 2 ). 
     
     
         3 . The article of  claim 1 , wherein hafnium from the hafnium disilicide is configured to be incorporated into a TGO layer that forms between the intermediate coating and the silicon-containing ceramic substrate and react with silicon dioxide of the TGO layer to form hafnium silicate (HfSiO 4 ). 
     
     
         4 . The article of  claim 1 ,
 wherein the silicon-containing ceramic substrate comprises:
 a ceramic matrix composite (CMC) substrate; and 
 a silicon-containing bond coat overlying the ceramic matrix composite (CMC), and 
   wherein the intermediate coating is overlying the bond coat.   
     
     
         5 . The article of  claim 1 ,
 wherein the silicon-containing ceramic substrate comprises a silicon-containing ceramic matrix composite (CMC) substrate, and   wherein the intermediate coating is overlying the silicon-containing CMC substrate.   
     
     
         6 . The article of  claim 1 ,
 wherein the intermediate coating includes a top portion proximate to the barrier coating and a bottom portion proximate to the silicon-containing ceramic substrate, and wherein a volume fraction of hafnium disilicide in the top portion is greater than a volume fraction of hafnium disilicide in the bottom portion.   
     
     
         7 . The article of  claim 1 , wherein the barrier coating comprises an environmental barrier coating (EBC). 
     
     
         8 . The article of  claim 7 , wherein the EBC comprises at least one of a rare earth (RE) disilicate, RE monosilicate, a RE disilicate and RE monosilicate mixture, a RE disilicate and silicon dioxide mixture, mullite, or BSAS. 
     
     
         9 . The article of  claim 1 ,
 wherein the intermediate layer comprising a first intermediate layer,   wherein the article further comprises a second intermediate layer overlying the first intermediate layer, and   wherein the second intermediate coating includes hafnium dioxide (HfO 2 ).   
     
     
         10 . The article of  claim 1 , wherein the coating system further comprises an abradable coating overlying the barrier coating. 
     
     
         11 . A method of forming a coating system, comprising:
 forming an intermediate coating on a silicon-containing ceramic substrate, wherein the intermediate coating includes silicon (Si) and hafnium disilicide (HfSi 2 ), and wherein a coefficient of thermal expansion (CTE) of the intermediate coating is less than about 7 parts per million (ppm) per degree Kelvin (K); and   forming a barrier coating on the intermediate coating.   
     
     
         12 . The method of  claim 11 , further comprising heating the intermediate coating to convert at least a portion of the hafnium disilicide to hafnium dioxide (HfO 2 ) and at least a portion of the silicon to silicon dioxide (SiO 2 ). 
     
     
         13 . The method of  claim 12 , wherein the barrier coating is formed on the intermediate coating after heating the intermediate coating. 
     
     
         14 . The method of  claim 11 , wherein hafnium from the hafnium disilicide is configured to be incorporated into a TGO layer that forms between the intermediate coating and the silicon-containing ceramic substrate and react with silicon dioxide of the TGO layer to form hafnium silicate (HfSiO 4 ). 
     
     
         15 . The method of  claim 11 ,
 wherein the silicon-containing ceramic substrate comprises:
 a ceramic matrix composite (CMC) substrate; and 
 a silicon-containing bond coat overlying the CMC substrate, and 
   wherein forming the intermediate coating on the silicon-containing ceramic substrate comprises forming the intermediate coating on the silicon-containing bond coat.   
     
     
         16 . The method of  claim 11 ,
 wherein the silicon-containing ceramic substrate comprises a silicon-containing ceramic matrix composite (CMC) substrate, and   wherein forming the intermediate coating on the silicon-containing ceramic substrate comprises forming the intermediate coating on the silicon-containing CMC substrate.   
     
     
         17 . The method of  claim 11 ,
 wherein the intermediate coating includes a top portion proximate to the barrier coating and a bottom portion proximate to the silicon-containing ceramic substrate, and   wherein a mol fraction of hafnium disilicide in the top portion is greater than a mol fraction of hafnium disilicide in the bottom portion.   
     
     
         18 . The method of  claim 11 , wherein the barrier coating comprises an environmental barrier coating (EBC). 
     
     
         19 . The method of  claim 18 , wherein the EBC comprises at least one of a rare earth (RE) disilicate, RE monosilicate, a RE disilicate and RE monosilicate mixture, a RE disilicate and silicon dioxide mixture, mullite, or BSAS. 
     
     
         20 . The method of  claim 11 ,
 wherein the intermediate coating comprises a first intermediate coating,   wherein the method further comprises forming a second intermediate coating overlying the first intermediate coating, and   wherein the second intermediate coating includes hafnium dioxide (HfO 2 ).